The present invention relates generally to transistor receiver circuits and, more particularly, to a chip-to-chip digital transmission circuit for delivering power over signal lines.
Differential signaling is often used in signal transmission where undesirable electrical noise may be induced on the transmission line. Such electrical noise in single-wire signaling can cause the signal voltage to rise above or fall below its acceptable threshold voltage, resulting in faulty switching at the receiving end. Differential signaling, on the other hand, simultaneously transmits two signals that are complements of each other. The logic state of a particular bit of information transmitted by a differential signal can be determined by taking the difference of the two signals' voltage levels. Since these two signals are transmitted on physically adjacent transmission lines, electrical noise induced on one line is also induced on the other. Undesirable noise therefore may affect the two signals, but the difference between the two remains substantially the same. The advantages of differential signaling are well known for conventional differential links.
A bi-directional link can be used in any situation where two devices must communicate with each other. A first communicating device can send data to a second communicating device, while the second communicating device can be sending data to the first communicating device. Alternatively, after the first device has completed one burst of data, the second communicating device can send data to the first communicating device. The advantages of bi-directional links over conventional methods include a reduction in the wiring between communicating devices and a reduction in the number of connector pins on each communicating device.
Over the last several years, CMOS-based (complementary metal-oxide semiconductor) integrated circuit (IC) technologies have been designed to operate with progressively lower power supply voltages with each passing generation. Lower supply voltages dictate lower voltage swings for the associated digital signals, which typically switch between ground and the power supply voltage. The benefits of using lower supply voltages include lower power consumption and faster signal switching times. However, Depending on the location of a communication path between chips, the attenuation of the path may be such that a certain level of power must be provided at the receiving end of the communication circuit. High-loss paths may require more power to be spent by the driver and receive circuits than is needed for some low-loss paths.
It would be desirable, therefore, to be able to provide a digital, chip-to-chip transmission circuit that can customize the level of power used for a specific communication path, and that can invest the circuit power only where it is needed.